Semaphore Implementation

Semaphore Synchronization Control
Semaphore Value: 1
Step: 0
Active: 0
Semaphore
1

Producers

P1
P2
P3

Consumers

C1
C2
C3
Shared Buffer Size: 5
Empty
Empty
Empty
Empty
Empty
Waiting Queue
Select a scenario and click Start to begin simulation

About Semaphores

A semaphore is a synchronization primitive used to control access to shared resources in concurrent programming.

  • Binary Semaphore: Can have values 0 or 1 (like a mutex)
  • Counting Semaphore: Can have any non-negative integer value
  • Wait (P): Decrements semaphore value, blocks if value becomes negative
  • Signal (V): Increments semaphore value, wakes up waiting processes

Semaphore Operations

wait(semaphore S) { S.value--; if (S.value < 0) { // Add process to waiting queue block(); } } signal(semaphore S) { S.value++; if (S.value <= 0) { // Remove process from waiting queue wakeup(); } }

Scenarios

Producer-Consumer:

  • Producers add items to buffer
  • Consumers remove items from buffer
  • Semaphores control buffer access and count

Reader-Writer:

  • Multiple readers can access simultaneously
  • Writers need exclusive access
  • Semaphores coordinate access patterns

Dining Philosophers:

  • Philosophers alternate between thinking and eating
  • Need two forks to eat
  • Semaphores prevent deadlock

Key Concepts

  • Mutual Exclusion: Only one process in critical section
  • Progress: Processes can enter critical section
  • Bounded Waiting: Finite wait time for processes
  • Deadlock Prevention: Avoid circular wait conditions

How to Use

  1. Select a scenario from the dropdown
  2. Click Start to initialize the simulation
  3. Use Step to execute one operation at a time
  4. Try Auto Demo for continuous execution
  5. Click Reset to start over

Watch how processes interact with semaphores and observe synchronization patterns!